Surgical instrument for impacting and extracting a cutting instrument

ABSTRACT

A surgical instrument including a cutting instrument for shaping a bone as well as an impaction/extraction device for use with the cutting instrument is disclosed.

BACKGROUND

1. Technical Field

The present disclosure relates to surgical instruments, and, moreparticularly, to surgical instruments for preparing the proximal end ofa tibia for receiving a tibial prosthesis.

2. Description of the Related Art

Orthopaedic prostheses are commonly utilized to repair and/or replacedamaged bone and tissue in the human body. For example, a kneeprosthesis used in total knee arthroplasty may include a tibial baseplate that is affixed to a resected or natural proximal tibia, a femoralcomponent attached to a resected or natural distal femur, and a tibialbearing component coupled with the tibial base plate and disposedbetween the base plate and femoral component. Prostheses frequently seekto provide articulation similar to a natural, anatomic articulation of aknee joint, including providing a wide range flexion.

To prepare the relevant bones of the human body to receive prostheticcomponents, a variety of cutting instruments are sometimes utilized. Inthe case of the proximal tibia, a bone saw may be utilized to prepare aplanar osteotomy of the proximal tibia which is then followed bydrilling of the intramedullary canal of the tibia to accommodate a stemextending from the base plate of a tibial prosthesis. Many tibialprostheses include a keel extending from opposing sides of the stem ofthe tibial prosthesis. To further shape the tibia to receive the tibialkeel, a broach is impacted into the proximal surface of the tibia tocreate a cavity sized to receive the keel of the tibial prosthesis.After impacting the broach, it must be extracted from the tibia whilemaintaining the shape of the cavity formed thereby.

When preparing the proximal tibia to receive a tibial prosthesis,instrumentation including a sizing plate may be utilized to facilitateforming a cavity in the tibia sized and shaped to accommodate the stemand keel of a tibial prosthesis that is properly positioned andoriented. The size of the sizing plate corresponds to the size of aprosthesis which is to be mated to the bone. The sizing plate ispositioned atop the proximal tibia after the initial, planar osteotomyis performed. Positioning of the sizing plate provides an indication ofthe location and orientation of the final prosthesis and guides thelocation of the subsequent bone shaping steps, i.e., drilling andbroaching, which are utilized to prepare the bone to receive the tibialprosthesis.

SUMMARY

The present disclosure provides a surgical instrument including acutting instrument for shaping a bone as well as an impaction/extractiondevice for use with the cutting instrument. The impaction/extractiondevice includes a housing having an internal wall defining alongitudinal cannula and a central shaft positioned in the longitudinalcannula of the housing. The central shaft is moveable longitudinallywithin the longitudinal cannula of the housing. The central shaft issecured or releasably securable to the cutting instrument so thatreciprocation of the central shaft within the housing can cause thecutting instrument to, alternatively, be impacted into or extracted froma bone. An extraction lever is pivotally connected to the housing andpresents a proximally facing impaction surface adjacent to an impactionsurface formed on a proximal end of the central shaft. The impactionsurface formed on the proximal end of the central shaft is alsoproximally facing. With this configuration, impaction of the impactionsurface of the central shaft as well as impaction of the impactionsurface of the extraction lever can be done by impacting or strikingthese surfaces with a mallet in a proximal to distal motion. Theextraction lever includes an extraction arm opposite the extractionlever and impaction surface, with the extraction arm positionable intocontact with a distal facing extraction surface formed on the centralshaft. In this configuration, impaction of the extraction leverimpaction surface positions the extraction arm in contact with theextraction surface of the central shaft and applies a distal to proximalforce to the central shaft to effect extraction of a tibial broach whichhas previously been impacted into the tibia.

The extraction lever impaction surface may be curved to facilitateimpaction of the same with a mallet moving in a proximal to distaldirection relative to the instrument. Specifically, as the extractionlever articulates to effect extraction of the broach from the tibia, thecurved surface ensures that no matter the rotational position of theextraction lever, the extraction lever impaction surface presents aproximally facing surface transverse to the longitudinal axis of thecentral shaft. Specifically, the extraction lever impaction surface ofthis form of the present invention defines a curve in a plane containingthe longitudinal axis of the central shaft and is substantially linearin a direction perpendicular to that plane. For the purposes of thisdescription, substantially linear is meant to encompass deviations fromlinear within manufacturing tolerances. With respect to the surgicalinstrument of the present disclosure, “proximal” and “distal” are usedwith reference to a user of the instrument. Specifically, “proximal”denotes a position of the instrument closest to a user of theinstrument, while “distal” refers to a portion of the instrumentfurthest from the user during use of the instrument.

When used in combination with a support structure such as a tibialsizing plate, the surgical instrument of the present invention mayincorporate at least one magnet positioned to attract the supportstructure to the housing of the surgical instrument as the supportstructure is indexed to the surgical instrument. Embodiments of thesurgical instrument of the present invention may further include a balldetent or spring clip operable to hold the central shaft in a retractedposition relative to the housing. The ball detent of this form of thepresent invention is useful in retracting the cutting instrument fromthe distal extent of the housing so that the surgical instrument can besecured to a support structure without interference from the cuttinginstrument.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features and advantages of this invention,and the manner of attaining them, will become more apparent and theinvention itself will be better understood by reference to the followingdescription of embodiments of the invention taken in conjunction withthe accompanying drawings, wherein:

FIG. 1 is a perspective view of a surgical instrument in accordance withthe present invention;

FIG. 2 is a radial elevational view of impaction/extraction instrumentin accordance with the present invention;

FIG. 3 is a cross-sectional view of the instrument illustrated in FIGS.1 and 2 taken along lines 3-3 of FIG. 1;

FIG. 4 is a partial view of the impaction/extraction instrumentillustrated in FIGS. 1-3, illustrating use of the same to impact acutting instrument;

FIG. 5 is a partial view of the impaction/extraction instrumentillustrated in FIGS. 1-3, illustrating use of the same to extract acutting instrument;

FIG. 6 is a perspective view of a tibial sizing plate useable to guidethe impaction/extraction instrument of the present invention; and

FIG. 7 is a sectional view illustrating a magnetic securement mechanismin accordance with the present invention.

Corresponding reference characters indicate corresponding partsthroughout the several views. The exemplifications set out hereindescribe and illustrate exemplary embodiments of the invention, and suchexemplifications are not to be construed as limiting the scope of theinvention in any manner.

DETAILED DESCRIPTION

Referring to FIGS. 1-3, impaction/extraction instrument 10 includeshousing 12 and central shaft 14. Referring to FIG. 3, housing 12includes internal wall 16 defining a longitudinal cannula spanningproximal end 18 and distal end 20 of housing 12. As illustrated in FIG.3, central shaft 14 is positioned within the cannula formed by internalwall 16. Internal wall 16 of housing 12 and the exterior of centralshaft 14 have complementary geometries, e.g., circular geometries, whichallow for axial reciprocation of central shaft 14 along its longitudinalaxis L relative to housing 12. Tibial broach 24 is secured to a distalend of central shaft 14.

Referring to FIGS. 2 and 3, central shaft 14 includes internal wall 22defining a T-shaped recess at a distal end of central shaft 14. Asillustrated in FIG. 3, internal wall 22 of central shaft 14 extendsperpendicular to longitudinal axis L of central shaft 14 such that theT-shaped recess formed by internal wall 22 of central shaft 14 isperpendicular to the longitudinal axis L of central shaft 14. Referringto FIG. 2, tibial broach 24 includes T-shaped protrusion 26 at aproximal end thereon. T-shaped protrusion 26 has a complimentarygeometry to the geometry of the T-shaped recess formed by internal wall22 of central shaft 14. Specifically, T-shaped recess 26 issubstantially congruent to the T-shaped recess formed by internal wall22 of central shaft 14 and is sized such that a close fit can be formedtherebetween. Referring to FIG. 3, central shaft 14 includeslongitudinal bore 28 which is intersected by transverse bore 30.Longitudinal bore 28 is sized to receive locating pin 32 as well asspring 34. As illustrated in FIG. 3, longitudinal bore 28 is exemplifiedas a stepped bore having a smaller diameter portion receiving spring 34and a larger diameter portion receiving locating pin 32. Locating pin 32includes proximal protrusion 36 which terminates distally at shoulder38. Proximal protrusion 36 is sized to be received within the interiorof spring 34. Shoulder 38 has a radial expanse greater than the radialexpanse of spring 34 so that spring 34 rests against shoulder 38.Locating pin 32 includes transverse bore 40 into which button 42 ispositioned. Button 42 is secured to locating pin 32 so that movement ofbutton 42 effects movement of locating pin 32. As illustrated in FIG. 3,spring 34 biases locating pin 32 distally such that button 42 abuts thedistal portion of the wall forming transverse bore 30.

At its distal end, locating pin 32 includes spherical distal end 44. Asillustrated in FIG. 3, spherical distal end 44 projects into theT-shaped recess defined by internal wall 22 of central shaft 14 in thenormally biased position of locating pin 32. Spherical end 44 oflocating pin 32 may be withdrawn from the T-shaped recess formed byinternal wall 22 of central shaft 14 by actuating button 42 proximallyso that locating pin 32 is moved against the spring biasing force ofspring 34.

To operably secure tibial broach 24 to impaction/extraction instrument10, button 42 is actuated proximally against the spring biasing force ofspring 34 to withdraw spherical distal end 44 of locating pin 32 fromthe T-shaped recess defined by internal wall 22 of central shaft 14.With spherical distal end 44 of locating pin 32 withdrawn from theT-shaped recess, T-shaped protrusion 26 of tibial broach 24 can bepositioned within the T-shaped recess formed by internal wall 22 ofcentral shaft 14. In this position, actuation of button 42 may cease sothat spring 34 biases locating pin 32 downwardly and spherical distalend 44 of locating pin 32 is positioned within divot 46 formed in aproximal end of tibial broach 24.

With tibial broach 24 secured to impaction/extraction instrument 10, thecentral shaft 14 can be pulled proximally relative to housing 12 to movetibial broach 24 proximally relative to housing 12 such that distal end48 of tibial broach 24 does not extend distally from distal end 20 ofhousing 12. In this way, the distal most extent of tibial broach 24 willnot extend beyond the distal most extent of housing 12 and, therefore,securement of impaction/extraction instrument 10 to a support structure,as will be further described hereinbelow, will not be interfered with bytibial broach 24. To hold tibial broach 24 in this retracted position,central shaft 14 includes divot 50 sized to receive ball 52 of a balldetent mechanism. As illustrated in FIG. 3, divot 50 can take the formof an annular groove extending about the circumference of central shaft14. With tibial broach 24 in the withdrawn position, ball 52 engagesdivot 50 to hold tibial broach in a position such that it does notextend beyond distal end 20 of housing 12. Divot 50 may, in alternativeembodiments, comprise a spherical divot sized to receive ball 52. Tomove tibial broach 24 from this position, impaction surface 54 may beimpacted by mallet 56 (FIG. 1).

The ball detent mechanism utilized to hold tibial broach 24 in itswithdrawn position includes transverse bore 58 intersecting internalwall 16 at opening 60. Opening 60 can be a circular opening having adiameter less than the diameter of ball 52. Positioned within transversebore 58 is spring 62 and set screw 64. In an alternative embodiment, setscrew 64 may be replaced with a cap which is welded in place withintransverse boar 58. In the finally seated position of set screw 64illustrated in FIG. 3, spring 62 is compressed against ball 52 such thatball 52 extends beyond opening 60 and into the longitudinal cannuladefined by internal wall 16 of housing 12. As central shaft 14 is movedproximally, ramp 66 formed on central shaft 14 engages ball 52 so thatball 52 is moved against the biasing force of spring 62 and withdrawnfrom the cannula defined by internal wall 16 of housing 12. As centralshaft 14 is moved further proximally such that ball 52 is aligned withdivot 50, biasing force of spring 62 positions ball 52 in divot 50 asdescribed hereinabove. The retracted position of tibial broach 24 isillustrated in FIG. 1.

A position of tibial broach 24 corresponding to its maximum extensiondistally from distal end 20 of housing 12 is illustrated in FIGS. 2 and3. In this position, extraction lever 68 can be utilized to apply adistal to proximal force to central shaft 14 and move central shaft 14and tibial broach 24 proximally. Extraction lever 68 is pivotallyconnected to housing 12 by cylindrical pivot pin 70. Cylindrical pivotpin 70 is pivotally received in a pivot aperture sized to allow rotationbut not radial translation of cylindrical pivot pin 70 relative to thepivot aperture. In the embodiment illustrated in FIG. 3, extractionlever 68 includes cylindrical aperture 72 into which cylindrical pivotpin 70 is positioned. In this embodiment, cylindrical aperture 72 issized to receive cylindrical pivot pin 70 to pivotally connectextraction lever 68 to housing 12, with cylindrical aperture 72 sized toallow rotation of extraction lever 68 relative to housing 12 but not toallow translation of extraction lever 68 in a direction orientedradially from cylindrical pivot pin 70. In alternative embodiments,cylindrical pivot pin 70 may be fixedly secured to extraction lever 68but may be pivotally connected within a cylindrical aperture formed inyolk 84 (FIG. 1) in a similar fashion to the pivotal connection betweencylindrical pivot pin 70 and cylindrical aperture 72 described above.

On opposing sides of cylindrical pivot pin 70, extraction lever 68includes extraction lever impaction surface 74 and extraction arm 76.Extraction lever impaction surface 74 faces proximally, away from distalend 20 of housing 12. Because extraction lever impaction surface 74faces proximally, it can be impacted by mallet 56 (FIG. 1) along atrajectory parallel to the impaction required to seat tibial broach 24,as will be further described hereinbelow.

Extraction arm 76 resides within slot 78 formed in central shaft 14. Asillustrated in FIG. 3, slot 78 terminates proximally in extractionsurface 80. Extraction surface 80 faces distally, away from impactionsurface 54 which forms the proximal end of impaction/extractioninstrument 10. With this arrangement, impaction of extraction leverimpaction surface 74 with mallet 56 positions extraction arm 76 tocontact extraction surface 80 and apply a distal to proximal force tocentral shaft 14 which will tend to pull tibial broach 24 proximallyfrom the position illustrated in FIG. 3 toward the withdrawn positionillustrated in FIG. 1. Movement of extraction arm 76 relative to housing12 is accommodated by slot 82 formed in housing 12.

Referring to FIG. 3, extraction lever impaction surface 74 has aradially outward most extent relative to longitudinal axis L of centralshaft 14 illustrated as distance D. Distance D measures no more than 10cm. With extraction lever impaction surface 74 spaced no more than 10 cmfrom longitudinal axis L of central shaft 14, the torque imparted toimpaction/extraction instrument 10 when mallet 56 strikes extractionlever impaction surface is minimized and therefore toggling of tibialbroach 24 within the broached bone will be minimized. Furthermore, thecenter of impaction surface 74 is spaced approximately 25 mm from thecenter of cylindrical pivot pin 70. With an expected impaction force onthe extraction head of approximately 7 kN, this would result in a torqueabout the center of cylindrical pivot pin 70 of about (7,000 N)×(0.025m)=175 Nm. The inventors of the present invention have concluded that atorque of less than 300 Nm is desired to prevent toggling of tibialbroach 24 during extraction thereof. In certain embodiments of thepresent invention, distance D can be as little as 5 cm. In alternativeembodiments of the present invention, distance D can be any valuebetween 5 and 10 cm in 0.5 cm increments, i.e., 5.0, 5.5, 6.0, 6.5, 7.0,7.5, 8.0, 8.5, 9.0, 9.5 or 10.0 cm.

In an exemplary embodiment of the present invention, the lever ratio ofthe extraction lever is approximately 1.6:1. What this means is that thelength of the arm extending from the center of cylindrical pivot pin 70to a terminal end of extraction lever 68 adjacent to extraction leverimpaction surface 74 is approximately 1.6 times the length of extractionarm 76 from the center of cylindrical pivot pin 70 to a second terminalend of extraction lever 68 on extraction arm 76. The inventors of thepresent application have determined that a lever ratio of extractionlever 68 anywhere between 3:1 to 1:1 strikes an appropriate balancebetween decreasing toggling of tibial broach 24 during extraction whilealso providing an instrument actuateable with a comfortable amount offorce applied by the user.

Extraction lever impaction surface 74 defines a curve in a planecontaining the longitudinal axis of central shaft 14. The section planealong which FIG. 3 is taken is such a plane. As illustrated in FIG. 3,extraction lever impaction surface 74 is curved in a plane containinglongitudinal axis L of central shaft 14. While extraction leverimpaction surface 74 is curved in a plane containing longitudinal axis Lof central shaft 14, it is substantially linear in a directionperpendicular to such plane. “Substantially linear” is meant toencompass linear configurations and those configurations withinmanufacturing tolerances of being linear. What this means is that inplanes parallel to the plane along which the cross-sectional view ofFIG. 3 is taken, the profile of extraction lever impaction surface 74remains unchanged. Curving of extraction lever impaction surface 74facilitates articulation of extraction lever 68 by impacting extractionlever impaction surface 74 with mallet 56. Specifically, the curvatureof extraction lever impaction surface 74 means that mallet 56 can beactuated in a proximal to distal direction d as illustrated in FIG. 5while maintaining good contact with extraction lever impaction surface74 throughout a full range of motion of extraction lever 68.

Referring to FIG. 1, impaction/extraction instrument 10 can be utilizedto broach tibia T in the following manner. After initially osteotomizingproximal surface P of tibia T, tibial sizing plate 86 is chosen,oriented with respect to tibial T and secured thereto. Techniques forosteotomizing proximal surface P of tibia T can include securing a cutguide to tibia T which guides an oscillating saw to cut proximal tibiaT. Examples of such techniques can be found in the Zimmer NexGen LPSFixed Knee Surgical Technique bearing copyright dates of 2002, 2008, theentire disclosure of which is hereby explicitly incorporated byreference herein. Alternative techniques for osteotomizing the proximaltibia and utilizing a sizing plate can be found in the Zimmer NexGen CRFlex and LPS Flex Knees Surgical Technique with posterior referencinginstrumentation bearing copyright dates of 2010, 2011 and the ZimmerNexGen MIS Tibial Component Cemented Surgical Technique bearingcopyright dates of 2005, 2006, 2008, 2009 and 2010, the entiredisclosures of which are hereby explicitly incorporated by referenceherein. Additionally, preparation of a tibia to receive a tibialprosthesis is shown and described in U.S. Pat. No. 5,634,927, assignedto the assignee of the present disclosure, the entire disclosure ofwhich is hereby explicitly incorporated by reference herein.

After pinning tibial sizing plate 86 to tibia T, impaction/extractioninstrument 10 can be indexed to tibial sizing plate 86 so thatimpaction/extraction instrument 10 is supported and guided by tibialsizing plate 86. Referring to FIGS. 2 and 7, impaction/extractioninstrument 10 includes bosses 88 extending distally from distal ends 20of housing 12. Bosses 88 are sized, shaped and spaced to cooperate withapertures 90 (FIG. 6) in tibial sizing plate 86 to indeximpaction/extraction instrument 10 to tibial sizing plate 86. In aportion of housing 12 adjacent to each boss 88, a chamber holds a magnet92 as illustrated in FIG. 7. Magnets 92 are oriented relative to theirrespective bosses 88 such that when each boss 88 is positioned within anaperture 90 to index impaction/extraction instrument 10 to tibial sizingplate 86, magnet 92 will be positioned over a proximal surface of tibialbase plate 86. When using a metallic base plate 86, magnets 92 will drawtibial sizing plate 86 toward impaction/extraction instrument 10 andfacilitate indexing of impaction/extraction instrument 10 to tibialsizing plate 86. During this process of indexing impaction/extractioninstrument 10 to tibial sizing plate 86, tibial broach 24 can maintainthe extracted position illustrated in FIG. 1 so that it cannot interferewith the indexing process.

With impaction/extraction instrument 10 properly indexed to tibialsizing plate 86, mallet 56 may be utilized to strike impaction surface54 to seat tibial broach 24 in tibia T and create an aperture in tibia Tsized to accommodate the keel of a tibial prosthesis. Specifically,while using one hand to grasp housing 12, a surgeon may use his or herother hand to actuate mallet 56 so that its head collides with impactionsurface 54 to impact the impaction surface and effect seating of tibialbroach 24 in tibia T. Prior to broaching tibia T, aperture 94 may beformed in tibia T to accommodate distal end 48 of tibial broach 24. Asdistal end 48 of tibial broach 24 enters aperture 94, teeth 96 of tibialbroach 24 contact the bone of tibia T and effect cutting of the same.Final seating of tibial broach 24 is signaled when undersurface 98opposing impaction surface 54 contacts proximal end 18 of housing 12 asillustrated in FIGS. 3 and 4. In this position, mallet 56 may beutilized to provide an impaction force to extraction lever impactionsurface 74 as illustrated in FIG. 5. Such impaction force creates atorque about the center of cylindrical pivot pin 70 (FIG. 3) andgenerates an extraction force in a distal to proximal direction alonglongitudinal axis L of central shaft 14.

While this invention has been described as having an exemplary design,the present invention can be further modified within the spirit andscope of this disclosure. This application is therefore intended tocover any variations, uses, or adaptations of the invention using itsgeneral principles. Further, this application is intended to cover suchdepartures from the present disclosure as come within known or customarypractice in the art to which this invention pertains and which fallwithin the limits of the appended claims.

What is claimed is:
 1. A surgical instrument, comprising: a cuttinginstrument for shaping a bone; a housing having an internal walldefining a longitudinal cannula; a central shaft positioned in saidlongitudinal cannula of said housing, said central shaft having alongitudinal axis, said central shaft moveable within said longitudinalcannula of said housing relative to said housing along said longitudinalaxis of said central shaft, said central shaft having a proximal end anda distal end securable to said cutting instrument; an impaction surfacefacing proximally, away from a distal end of the surgical instrument,said impaction surface forming said proximal end of said central shaft,whereby impacting said impaction surface applies a proximal to distalforce to said central shaft; an extraction lever pivotally connected tosaid housing, said extraction lever having an extraction lever impactionsurface facing proximally, away from a distal end of the surgicalinstrument, said extraction lever impaction surface moveable relative tosaid central shaft, said extraction lever having an extraction armopposite said extraction lever impaction surface, said central shafthaving an extraction surface facing distally away from a proximal end ofthe surgical instrument, said extraction arm positionable to contactsaid extraction surface, whereby impacting said extraction leverimpaction surface positions said extraction arm in contact with saidextraction surface and applies a distal to proximal force to saidcentral shaft.
 2. The surgical instrument of claim 1, wherein saidextraction lever impaction surface defines a curve in a plane containingthe longitudinal axis of the central shaft, said impaction surface beingsubstantially linear in a direction perpendicular to said plane.
 3. Acombination, comprising the surgical instrument of claim 1 and ametallic support structure having a support structure indexing feature,said housing having a housing indexing feature, said support structureindexing feature and said housing indexing feature selectably engageableto index the surgical instrument to the support structure, said housingincorporating at least one magnet positioned to attract said metallicsupport structure to said housing as said housing indexing feature inbrought into engagement with said support structure indexing feature. 4.The combination of claim 2, wherein said support structure comprises atibial sizing plate and wherein said cutting instrument comprises atibial broach.
 5. The surgical instrument of claim 1, wherein saidhousing includes a transverse bore intersecting said longitudinalcannula of said housing at an opening, said surgical instrument furthercomprising: a ball detent positioned in said transverse bore andextending into said longitudinal cannula of said housing, said balldetent having a diameter larger than a diameter of said opening; aspring positioned in said transverse bore and biasing said ball detenttoward said opening; said central shaft including a divot sized toreceive said ball detent, whereby, with said ball detent positioned insaid divot, movement of said central shaft relative to said housing isresisted, whereby, with said cutting instrument secured to said centralshaft and with said ball detent positioned in said divot, said cuttinginstrument does not extend distally beyond a distal extent of saidhousing.
 6. The surgical instrument of claim 1, wherein said extractionlever impaction surface is spaced no more than 10 cm from saidlongitudinal axis of said central shaft.
 7. The surgical instrument ofclaim 1, further comprising: a cylindrical pivot pin pivotally receivedin a pivot aperture sized to allow rotation but not radial translationof said cylindrical pivot pin relative to said pivot aperture, saidcylindrical pivot pin pivotally connecting said extraction lever to saidhousing.
 8. The surgical instrument of claim 7, wherein said extractionlever extends a first distance from a center of said cylindrical pivotpin to a first terminal end of the extraction lever adjacent to theextraction lever impaction surface and said extraction lever extends asecond distance from said center of said cylindrical pivot pin to asecond terminal end of the extraction lever on the extraction arm, aratio of said first distance to said second distance being in the rangeof 3:1 to 1:1.
 9. The surgical instrument of claim 8, wherein said ratioof said first distance to said second distance equals 1.6:1.
 10. Thesurgical instrument of claim 1, wherein said distal end of said centralshaft includes a central shaft securement feature, said cuttinginstrument including a cutting instrument securement feature matablewith said central shaft securment feature to releasably secure saidcutting instrument to said central shaft.
 11. The surgical instrument ofclaim 10, wherein said central shaft securement feature comprises a walldefining a T-shaped recess and a locating pin having a spherical distalend, said locating pin moveable within said T-shaped recess, and saidcutting instrument securement feature comprises a T-shaped protrusionshaped to be received within said T-shaped recess of said central shaftand a divot sized to receive said spherical distal end of said locatingpin, whereby, with said T-shaped protrusion positioned in said T-shapedrecess and said spherical distal end of said locating pin positioned insaid divot, movement of said cutting instrument relative to said centralshaft is resisted.
 12. A surgical instrument, comprising: a cuttinginstrument for shaping a bone; a housing having an internal walldefining a longitudinal cannula; a central shaft positioned in saidlongitudinal cannula of said housing, said central shaft having alongitudinal axis, said central shaft moveable within said longitudinalcannula of said housing relative to said housing along said longitudinalaxis of said central shaft, said central shaft having a proximal end anda distal end securable to said cutting instrument; an impaction surfacefacing proximally, away from a distal end of the surgical instrument,said impaction surface forming said proximal end of said central shaft,whereby impacting said impaction surface applies a proximal to distalforce to said central shaft; an extraction lever pivotally connected tosaid housing, said extraction lever having an extraction lever impactionsurface facing proximally away from a distal end of the surgicalinstrument, said extraction lever impaction surface defining a curve ina plane containing the longitudinal axis of the central shaft, saidimpaction surface being substantially linear in a directionperpendicular to said plane, said extraction lever having an extractionarm opposite said extraction lever impaction surface, said central shafthaving an extraction surface facing distally, away from a proximal endof the surgical instrument, said extraction arm positionable to contactsaid extraction surface, whereby impacting said extraction leverimpaction surface positions said extraction arm in contact with saidextraction surface and applies a distal to proximal force to saidcentral shaft.
 13. A combination, comprising the surgical instrument ofclaim 12 and a metallic support structure having a support structureindexing feature, said housing having a housing indexing feature, saidsupport structure indexing feature and said housing indexing featureselectably engageable to index the surgical instrument to the supportstructure, said housing incorporating at least one magnet positioned toattract said metallic support structure to said housing as said housingindexing feature in brought into engagement with said support structureindexing feature.
 14. The combination of claim 13, wherein said supportstructure comprises a tibial sizing plate and wherein said cuttinginstrument comprises a tibial broach.
 15. The surgical instrument ofclaim 12, wherein said housing includes a transverse bore intersectingsaid longitudinal cannula of said housing at an opening, said surgicalinstrument further comprising: a ball detent positioned in saidtransverse bore and extending into said longitudinal cannula of saidhousing, said ball detent having a diameter larger than a diameter ofsaid opening; a spring positioned in said transverse bore and biasingsaid ball detent toward said opening; said central shaft including adivot sized to receive said ball detent, whereby, with said ball detentpositioned in said divot, movement of said central shaft relative tosaid housing is resisted, whereby, with said cutting instrument securedto said central shaft and with said ball detent positioned in saiddivot, said cutting instrument does not extend distally beyond a distalextent of said housing.
 16. The surgical instrument of claim 12, whereinsaid extraction lever impaction surface is spaced no more than 10 cmfrom said longitudinal axis of said central shaft.
 17. The surgicalinstrument of claim 12, further comprising: a cylindrical pivot pinpivotally received in a pivot aperture sized to allow rotation but notradial translation of said cylindrical pivot pin relative to said pivotaperture, said cylindrical pivot pin pivotally connecting saidextraction lever to said housing.
 18. The surgical instrument of claim12, wherein said extraction lever extends a first distance from a centerof said cylindrical pivot pin to a first terminal end of the extractionlever adjacent to the extraction lever impaction surface and saidextraction lever extends a second distance from said center of saidcylindrical pivot pin to a second terminal end of the extraction leveron the extraction arm, a ratio of said first distance to said seconddistance being in the range of 3:1 to 1:1.
 19. The surgical instrumentof claim 18, wherein said ratio of said first distance to said seconddistance equals 1.6:1.
 20. A method of shaping a bone to receive aprosthetic component, comprising the steps of: providing a cuttinginstrument; providing an impaction/extraction instrument having a distalend and a proximal end, the proximal end having an impaction surface,the impaction surface facing proximally away from the distal end of theimpaction/extraction instrument, the impaction/extraction instrumenthaving an extraction surface facing proximally away from the distal endof the impaction/extraction instrument; securing said cutting instrumentto said distal end of the impaction/extraction instrument; impacting theimpaction surface to seat the cutting instrument in the bone by applyinga proximal to distal force to the impaction surface; and impacting theextraction surface to unseat the cutting instrument from the bone byapplying a proximal to distal force to the extraction surface.
 21. Themethod of claim 20, further comprising the steps of: providing ametallic support structure; indexing the impaction/extraction instrumentto the support structure, the impaction/extraction instrument having amagnet disposed adjacent to the distal end, the magnet drawing themetallic support structure into engagement with the impaction/extractioninstrument during said indexing step.
 22. The method of claim 21,further comprising the steps of: withdrawing the cutting instrument intoa withdrawn position so that it does not extend distally from the distalend of the impaction/extraction instrument; and holding the cutting inthe withdrawn position during said step of indexing theimpaction/extraction instrument to the support structure.